Corrected entry: The three characters are playing with Legos near the beginning of the film. They are sitting next to a mirror, and we see Andrew building his Lego structure. Andrew is reflected in the mirror but the Lego structure is not, indicating the use of CGI.
manthabeat
12th Feb 2012
Correction: Matt is sitting in front of the mirror in the position where the reflection of the Lego would be, and therefore obscures the view at that position.